Effective influenza A vaccines represent a major public health need, both to combat annual virus outbreaks in at-risk populations, and also to protect against possible pandemic infection by new strains, including highly pathogenic avian influenza A (H5N1) strains. Human clinical trials have shown that baculovirus-expressed recombinant hemagglutinins (rHA) can elicit serum antibody responses in both healthy and elderly adults. However, because the HA is administered as a soluble protein without adjuvant, relatively high doses have been required to achieve protective immunity;this has been a particular problem for the H5 rHA as well as for egg-derived H5 vaccines in humans. Moreover, recent work has suggested that alum, the most widely available adjuvant for vaccines in humans, will not have a significant dose-sparing effect for H5 vaccines in man. As a result, alternative approaches are urgently needed to increase the immunogenicity of H5 vaccines, and decrease the dose needed to achieve protective immunity. Display of proteins or peptides in an ordered, repetitive array can lead to greatly increased immune responses, compared to immunization with soluble protein antigens. Bacteriophage particles are well- recognized for their ability to permit the display of short, exogenous peptides at high copy number in a quasicrystalline array that facilitates antibody production through cross-linking of surface immunoglobulins. The central hypothesis of this proposal is that influenza A virus vaccine approaches can be improved, by using lambda phage as a scaffold to display viral antigens in a highly immunogenic context. We propose to achieve this by using a simple in vitro complementation system to "decorate" phage particles with baculovirus-produced H5 rHA. Proof-of-principle experiments will be conducted to explore the effectiveness of this novel approach. In the first aim, H5 rHA will be displayed on the lambda phage capsid. This will be achieved by expressing translational fusions between the major lambda phage coat protein, gpD, and the H5 hemagglutinin (HA) in insect cells, and then using this material to decorate preformed, gpD-deficient phage capsids. In the second aim, a mouse model system will be used to assess the immunogenicity of lambda phage particles displaying H5 rHA. These experiments will assess humoral immune responses to H5 HA, and will compare results to those elicited by purified, recombinant H5 rHA alone. Finally, live virus challenge studies will be conducted, in order to test the protective effectiveness of the elicited immune responses. Collectively, these experiments are expected to provide proof-of-concept data in support of our hypothesis that the lambda phage scaffold will allow for the generation of strong antibody responses to influenza virus antigens, such as H5 HA. This application is aimed at developing a new and improved method to develop vaccines for influenza viruses, including the highly pathogenic avian influenza viruses that are a major domestic and global health concern. The approach we are proposing has the potential to both increase the immunogenicity as well as decrease the dose of these vaccines, and at the same time utilizes an inexpensive and relatively simple technology that could easily be adapted for use on a large scale.